This invention relates to a dielectric resonator device used mainly in high-power high-frequency radio equipment.
2. Description of the Prior Art
Heretofore, the dielectric resonator device has been often used in high-frequency radio equipment as a resonator which has a high Q factor not only in the microwave band but also in the UHF band.
A conventional dielectric resonator device is constructed such that a cylindrical dielectric resonator to which a dielectric support is bonded with the use of glass is fixed within a metal case provided with a loop-like electrode loop through which high-frequency signals are received and delivered, by screwing the dielectric support, and an opening of the metal case is closed by a metal cover having a tuning screw so as to shield the device. The dielectric resonator is magnetically combined with the loop-like electrode so as to resonate at a specific frequency determined by the dielectric constant, the shape of the resonator and the type of resonance mode to be used. Adjustment of the resonance frequency is performed by moving the tuning screw to and away from the dielectric resonator. It is possible to reduce the size of the dielectric resonator device by increasing the dielectric constant of the resonator.
On the other hand, it is possible to make the dielectric resonator device operate as a band-pass filter by providing two electrodes which serve as input/output terminals, respectively. The filter of such construction is widely used as the channel filter of the transmitter multiplexer equipped in the mobile radio base station as shown in the literature, for example (K. Wakino, et al., "800 MHz band miniaturized channel dropping filter using low loss dielectric resonator", Denshi Tokyo No. 24, 1985, pp. 72-75).
In the dielectric resonator device, electromagnetic energy for resonation is stored inside the dielectric resonator and in the vicinity thereof. For this reason, when a metal conductor is brought close to the dielectric resonator, high-frequency current flows on the surface of the conductor so as to cause a loss in electromagnetic energy due to resistance, thereby deteriorating the characteristics of the resonator. Therefore, it is necessary to consider that the internal structure of the metal case of the dielectric resonator device is so designed as not to allow any metal to approach the dielectric resonator, in order to prevent a loss in electromagnetic energy.
Further, a part of the electromagnetic energy stored inside and in the vicinity of the dielectric resonator is converted into heat within the dielectric resonator and the dielectric support due to a dielectric loss. The dielectric support is made of a material which has a small dielectric constant and causes less high-frequency loss, and it is designed such that most of the electromagnetic energy is stored in the dielectric resonator which exhibits a large dielectric constant so that the dielectric loss is almost caused in the dielectric resonator.
Heat generated in the dielectric resonator is radiated by way of the following two routes. One of them is to radiate heat from the dielectric support due to heat conduction, and the other one is to radiate heat from the surface of the dielectric resonator through the air within the metal case. However, in addition to the above conditions, there is a certain condition in selecting the material of the dielectric support such that the coefficient of thermal expansion of the material must be identical with that of the dielectric resonator because they are bonded to each other by use of glass. None of the dielectric materials of high heat conductivity which are known at present satisfy these conditions. In consequence, in the dielectric resonator of the conventional structure, the amount of heat radiated from the dielectric support was very small. Further, in such a case that the dielectric resonator is reduced in size while the dielectric constant or working frequency thereof is increased, it becomes difficult to radiate heat from the surface of the dielectric resonator since the surface area thereof is small.
In the dielectric resonator device of such construction, when a high-power high-frequency signal is fed thereto, the temperature of the dielectric resonator rises to cause problems including an increase in high-frequency loss and a drift of resonance frequency of the dielectric resonator.
In order to solve the above-mentioned problems, there has hitherto been proposed a method in which bar dielectrics are inserted into a drum dielectric resonator from above and below and fixed thereto so as to radiate heat as disclosed in Japanese patent Unexamined publication No. 1-109802. This method, however, has problems wherein (1) dimensional accuracy of the drum dielectric resonator and the bar dielectrics and the roughness of the contact surface make it difficult to reduce the contact thermal resistance, (2) it is impossible to extend the frequency variable range since the tuning mechanism and the resonator cannot be opposed to each other from the viewpoint of structure, and (3) it is not applicable to the cylindrical dielectric resonator.